JPH01103907A - Manufacture of high purity substance from silicon, nitrogen and hydrogen - Google Patents

Abstract

PURPOSE: To produce a high purity Si₃N₄ by allowing an elemental Si to react with a liq. nitrogen-hydrogen reaction product at low temp.

CONSTITUTION: An intermediate reaction product consisting of Si, N₂ and H₂ is obtained by allowing the mixture to react at ≤200°C for 30 min-100 hr in atmospheric pressure after milling the nitrogen-hydrogen reaction product expressed by formula ((n) is 1-4, when the nitrogen-hydrogen reaction product is a linear compd., (m) is 2; and when the reaction product is a cyclic compd., (m) is 0) and 99.9 wt.% elemental Si (when (n) is 1) or 95 wt.% elemental Si (when (n) is 2-4) having 0.01-150 μm grain size. Then the reaction product is heated at a temperature of 1,200-1,700°C for 15 min-2 hr in a nonreactive atmosphere to obtain the Si₃N₄ of ≥99.9 wt.% purity.

COPYRIGHT: (C)1989,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION The present invention provides an improved method for producing high purity silicon nitride that includes producing a novel liquid solution having silicon, hydrogen and nitrogen dissolved therein. It is related to. This novel liquid solution can be used as an intermediate in various chemical synthetic preparations, including as a precursor for the production of silicon nitride.

More specifically, the present invention provides silicon,
The present invention relates to producing high purity silicon nitride by producing a high purity intermediate material consisting of nitrogen and hydrogen and heating the intermediate material.

Silicon nitride is an important structural material with potential for use in high strength applications such as aerospace alloy cutting tools and ball bearings. Currently, this material is
It is intended for use in high temperature environments such as in turbine blades and ceramic diesel engines. Also,
The dielectric properties of this material make silicon nitride an important component in semiconductor barriers.

Using elemental silicon, which is highly pure and inexpensively available,
This elemental silicon is reacted in a continuous automated process with a liquid state nitrogen-hydrogen reactant at ambient temperature to produce a high purity intermediate product consisting of silicon, nitrogen and hydrogen, and the resulting intermediate It is desired to develop an industrial method for producing high-purity silicon nitride, which can produce high-purity silicon nitride by directly heat-treating the product without adding any purification steps.

The first work to directly react elemental silicon with nitrogen compounds at low or high temperatures was published in “A Compreh.
intensive treatment on Inor
ganicand Theoretical Chem
Istry”, Vol. VI, New York
: Wllley, 1981. p, lB3, Nonakate J, W.

As cited by Mel for, E, Vlgo
Done by uroux. He discovered that at bright, scorching temperatures ammonia reacts with silicon to form nitrides with the liberation of hydrogen.

The high temperature nitriding reaction of silicon is described in U.S. Patent No. 4.235.85.
7, etc., and is well known. However, ultra-high purity silicon is difficult to nitride at high temperatures. This is because a nitride protective film (precisely of the type used on semiconductors for passivation) is produced. Jour
nal Electrochem.

5ociety, Vol, 123.197B, p
"Mass Speetr" published on p. 512-514.
ometric 5tudies on LightT
Empire Reaction Bet
ween IlydrogenChloride a
nd 5ilIca/sth 1con ” and Journal An+, CeraIIl,
Soc, Vol, 60 (1-2), 1977
'coIIlpara published in , pp, 7g-81
ttvStudles ol' Metal Add
tives on the N1trld-atio
In a paper entitled 'No ol'5ilicon', S, S,
LIn states that such nitriding processes require halide, iron, or other cationic catalysts. D. Campos-Loriz et al.
Urnal Mat, Sci, Vol. 14.1
979. The published in pp, 1007=008
Ef'f'ects orIlydrogen ont
he N1tridatlon o[' 5llico
In a paper entitled "n", also jl, Dervtsbego
vic et al., Journal Mat, Sci.

Vol, 1B, 1979. 'The Roleof' Ilydroge published in pp, 1945-55
n in the N1trldation
of SillconPowder Compact
In a paper titled ``S'', we further explore the effects of hydrogen and water vapor on the silicon nitridation reaction, at the expense of resolving the inertness and high cost of this process.

In the aforementioned Mellor article, p. 183, EJIgouroux is cited as an example of an unsuccessful attempt to react silicon with liquid ammonia at low temperatures. These findings have led researchers in this technical field to use more reactive silicon derivatives, such as silicon chloride, silane, etc., to produce 513N4 at temperatures below 100°C, which is the preferred temperature range for industrial processes. made me think I would have to use .

Silicon nitride is therefore now produced industrially on a large scale by the low temperature reaction of silicon tetrachloride with liquid ammonia as described in US Pat. No. 4,198,178. The amorphous silicon diimide intermediate can be crystallized to alpha silicon nitride by heat treatment in a nitrogen atmosphere. However, the resulting product does not have the purity required for the desired uses as mentioned above due to residual chloride on the particle surface. Removal of halides from the final product by lengthy extraction processes with liquid ammonia or vacuum processing requires additional processing costs. Also, during this purification operation, oxygen contamination occurs due to air and moisture sensitivity of the imide intermediate. Even when silicon tetrachloride and ammonia are reacted in the gas phase at temperatures above 700° C., chlorine and oxygen contamination cannot be sufficiently removed. Am.

Ceram, Soc, Bull,, Vol, 65
(8) 198B, pp.

M, Rahao+an et al. published in 1171-76 “
Sur['aceCharacterization
of 5ilicon N1tride andS
llcon Carbide Powders”.

It is well known to use silicon halides as a silicon source and react them with nitrogen-containing substances to form silicon nitride. Such reactions are described in numerous U.S. patents, such as U.S. Pat.
No. 845, same No. 4. l13.830', 4.12
2.220, 4,145.224, 4.2
No. 08.215, No. 4.368,180, No. 4,
No. 376.652, No. 4.399.115, etc.

It has also been proposed to use silane as a silicon source and react it with a nitrogen compound to produce silicon nitride. U.S. Patent No. 4.122,155, U.S. Patent No. 4.348
．． No. 068, No. 4.387.079, No. 4.61
No. 2.297 teaches the use of silane as the silicon source in such reactions.

Silane (S iH4) is a gas that is highly reactive at temperatures above 12°C, but it is explosive, requires a long time to deposit the product, and does not contain enough stoichiometry or morphology. There are problems such as uncontrollability and high cost of the entire process. Reactions with halogen-substituted silanes, as described in the last two US patents mentioned above, create impurity problems and require additional purification costs.

The synthesis of silicon nitride can be achieved at high temperatures (1000=700° C.) by carbothermic nitridation of silicon dioxide. This method is described in U.S. Pat. No. 4,122.152, U.S. Pat.

A method for producing silicon nitride from silicon mono- and di-sulfides and ammonia is described in U.S. Pat. No. 3.211.5.
In No. 27 and No. 4,552,740, high temperature is used. These synthetic reactions are more interesting than many of the high temperature methods mentioned above. This is because steam transfer and VLS
This is because high reactivity and various forms can be created depending on the mechanism. In addition, sulfur evaporates more cleanly from the product.

Using available elemental silicon as a starting material of high purity, the elemental silicon is reacted with a nitrogen-hydrogen reactant in a liquid state at a temperature corresponding to below 200°C, preferably below 100°C, at atmospheric pressure to produce silicon. It is desired to develop a method for producing high-purity silicon nitride by producing a high-purity intermediate product consisting of nitrogen and hydrogen and heat-treating the obtained intermediate product.

OBJECTS OF THE INVENTION It is therefore an object of the present invention to provide a method for producing high-purity silicon nitride by reacting elemental silicon with a reactive nitrogen-hydrogen compound in a liquid state at a temperature desirable for industrial use. It is to provide.

Another object of the invention is to produce high purity silicon nitride by an initial reaction of elemental silicon with a reactive liquid nitrogen-hydrogen reactant at low temperatures, i.e. below 200°C, preferably below 100°C. The purpose is to provide a method.

Yet another object of the invention is to combine high purity elemental silicon in granular form and high purity nitrogen-hydrogen reactant in liquid state at 20%
An object of the present invention is to provide a method for producing high-purity silicon nitride from an intermediate reaction product consisting of silicon, nitrogen, and hydrogen obtained by reaction at 0°C or lower, preferably 100°C or lower.

Yet another object of the invention is to provide a method for producing intermediate products consisting of silicon, nitrogen and hydrogen at temperatures below 100°C.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, granular high-purity elemental silicon is mixed with a high-purity nitrogen-hydrogen reactant in a liquid state at a temperature corresponding to 200° C. or lower, preferably 100° C. or lower, at atmospheric pressure. High-purity silicon nitride can be produced by first producing a high-purity intermediate produced by reacting as shown in the following reaction formula: Si+[NoH(n+1)]111→(Si, N, H ) In the intermediate formula, n=-4; m-2 when the nitrogen-hydrogen reactant is linear, and m=0 when the nitrogen-hydrogen reactant is cyclic.

An embodiment of the method of the invention is shown in the flow sheet of the accompanying drawings.

The high-purity reactive nitrogen-hydrogen liquefying compound used in this invention is hereinafter referred to as a [Nn H(n=-++)]1 reactant, and when n=, this compound converts into liquid ammonia (NH3). and when n-2 or more, it consists of hydrazine (NH). Preferred hydrazine
The rl+H n compound is N 2 H4. However, higher molecular weight hydrazines, such as triazine (N3
H5), tetrazine (N4HB), isotetrazine (N
4H6), cyclotriazine (N
3H3) and the like can also be used as reactive nitrogen-hydrogen liquids and are within the scope of this invention.

In order to obtain the desired high purity intermediate, high purity [NoH(
n+1. I)] 1 The purity of the reactant was determined to be less than 99.9
wt,%, preferably should be 99.995 vt,%. Liquid ammonia is readily available in such purity, for example by condensation from the corresponding gas. On the other hand, liquid anhydrous hydrazine (N2H4) of such a level of purity is commercially available as a U.S. military standard as a component of rocket fuel.

The other reactant consists of particulate elemental silicon. The reaction product of elemental silicon and liquid ammonia is a solid imide, which is not easily purified. Surprisingly, however, when reacted with liquid hydrazine, a clear liquid is produced which is readily amenable to chemical purification methods. Therefore, the use of liquid hydrazine eliminates the need for high-purity silicon starting materials and allows the use of relatively low-purity silicon, for example, 95 wt.% or more, which is economically preferable. For purification, well-known liquid purification methods such as distillation, solvent extraction, crystallization, etc. can be used.

As mentioned above, the silicon purity requirement is [NnH(n
+1ll)] 1 reactant is n=, but it depends on whether it is greater than 1. n-2-4 (Example 2 described later)
), it is not necessary to use high-purity silicon;
Silicon with a purity of 95 wt.% or greater can be used in this reaction. However, since the product produced by the reactant with n = (see Example 1 below) cannot be easily purified, it is necessary to use high-purity silicon when using liquid ammonia as the other reactant. There is. High purity silicon means silicon with a purity of 99.9 vt, % or higher, preferably 99.999 wt, %.

The particle size of the elemental silicon reactant is preferably about 10
0 meshes (Tyler) or less, or about 150
It is less than a micron. Larger particle sizes of silicon can be used to react with the [NnH(n+fll)]1 reactant, but for a fully efficient reaction, the silicon in contact with the reactive nitrogen-hydrogen liquid is It is important to increase the surface area. Larger silicon particles, such as chunks about 2.5 mm in diameter and with a small surface area, react at a slower rate. Such large particle silicon can be preferably used when the present invention is applied to an industrial process where reactants are continuously flowed. The lower limit of silicon particle size is determined by the availability of small particles and also by the safety limits in terms of ignitability of fine particles. From about 0.01 micron (colloidal) to about 100 mesh (Tyler), preferably about 0.01 micron (colloidal) to about 100 mesh (Tyler). Particle size range from OL to 150 microns
[NnH(n+
ll1)] yields particles that can quickly and completely react with the reactants.

Relatively large particle sizes, e.g. 100 mesh (Ty
When using larger particle sizes of silicon, the particles can be milled prior to the reaction, or in situ during the reaction, as described below, under conditions that do not reduce the desired purity. For example, relatively large silicon particles can be milled using large chunks of silicon as the milling agent.

Silicon is technically a metalloid, not a metal, so the term "elemental" refers to elemental silicon,
In other words, in order to specify that reduced silicon and not silicon compounds are referred to as high purity reactants,
As used herein in reference to silicon reactants.

According to the invention, the [NnH(n,+m)]1 reactant and the particulate elemental silicon reactant are heated at low temperatures, i.e. below the boiling point of the [NnH(n+Il)]1 reactant at the pressure used. temperature, preferably about 1 below the corresponding boiling point at the pressure used
The reaction is carried out at a temperature lower than 5°C to about 100°C. For example, if the reactive nitrogen-hydrogen liquid is ammonia, the reaction temperature at atmospheric pressure will be below -33°C. When hydrazine is used as a liquid reactant, the reaction temperature at atmospheric pressure is 113°C.
, preferably below about 98°C.

The term "low temperature" as used herein defines a temperature corresponding to below 200°C, preferably below 100°C at atmospheric pressure. This allows for 1000
The inventive method can be distinguished from conventional methods that use temperatures above .degree.

A preferred reaction temperature range when reacting ammonia is a temperature range corresponding to about -33°C to about -78°C at atmospheric pressure. The preferred reaction temperature range when reacting hydrazine (N2H4) is from about 0°C to about 75°C at atmospheric pressure.
, preferably in a temperature range corresponding to about 15°C to 50°C.

It should be noted that the above description of reaction temperatures indicates temperatures that correspond to the relevant temperatures at atmospheric pressure.

This is because reactions are often carried out at pressures other than atmospheric pressure. For example, when liquid ammonia is used as the reactant [NoH (. It's advantageous. Therefore, the reaction temperature ranges described herein are not absolute temperatures, but are a function of the pressure used.

The reaction time (residence time for continuous reactions) of the reactants is:
It will vary depending on the reactants, the temperature/pressure at which the reaction is conducted, and other reaction conditions described below. , a specified amount of reactant (e.g. [NnH(n+ll) 1150 ml and particle size 1
Reaction times for batch reactions containing micron silicon (5 g) vary from less than 1 hour to 100 hours, preferably from about 30 minutes to about 50 hours. If the silicon particle size is larger, a longer reaction time may be used, but more SiO2 will be formed on the surface. For example, a batch reaction of hydrazine and particulate elemental silicon at 25°C (atmospheric pressure) can be completed in a few hours, whereas a batch reaction of liquid ammonia and particulate elemental silicon can be completed in a few hours.
The batch reaction at °C (atmospheric pressure) is carried out for 48 hours.

According to a preferred embodiment of the invention, the reaction time can be shortened by applying a grinding or milling action during the reaction. This is believed to be because the reaction is promoted by constantly exposing new unreacted silicon surfaces and bringing them into contact with the [NnH(n+1)]1 reactant. For example, 100 meshes (Tyler)
When reacting silicon particles with liquid ammonia at -78°C at atmospheric pressure, the reaction time is reduced from more than 48 hours to less than 1 hour by milling the silicon particles during the reaction with the liquid ammonia reactant. be able to.

Such milling or attrition of elemental silicon removes the reactants of the elemental silicon surface (i.e., St
It functions to remove O2). Such coatings can be obtained by chemically treating the particulate silicon with a stripping reagent such as hydrofluoric acid or ammonium hydrogen fluoride and/or in a reducing atmosphere such as an argon/hydrogen atmosphere, optionally prior to reaction. By heat treatment to at least 1300° C., the reaction time can be considerably shortened, for example to less than 0.5 hours.

If such attrition or milling is carried out as part of the reaction, relatively large size elemental silicon particles, such as particles larger than a lOO mesh (Tyler), are used and are allowed to react while the reaction proceeds. It can also be crushed on the spot. The reaction can be carried out continuously, in which products are removed as they are produced, or it can be carried out intermittently. The use of large sized elemental silicon particles that are ground in situ during the course of the reaction is of particular value for continuous processes.

In this case, the liquid containing the intermediate products produced by the reaction is continuously removed from the reaction zone, and the large particles of elemental silicon that are to be further ground remain in place and continuously fresh [NnH(n
+1. l)] react with 1 reactant.

When the reaction is carried out batchwise, a stoichiometric excess of [NnH (. You can collect things. If a continuous process is used, the liquid containing both the intermediate product and the [NnH(n+1)]1 reactant is removed from the reaction zone, and the [NnH(.+1ll)]1 reactant is then transferred to the intermediate product. If necessary, it can be separated from the reactor and returned to the reaction zone.

The intermediate solution produced by this reaction consists of a solution or dispersion of silicon, nitrogen, and hydrogen;
= Contains impurities of 0 ppm or less. This intermediate product can be used in applications requiring one or more elements in the liquid state, such as turning polymers into fibers. The intermediate product obtained by this invention includes silicon,
It can also be used as a reagent in a wide range of chemistries to synthesize complex molecules containing nitrogen and hydrogen, and optionally other elements. Furthermore, this intermediate can also be used to produce silicon ceramics (eg silicon nitride or silicon carbide) via suitable reaction routes. For example, if this intermediate is heated to 800° C. in an argon atmosphere, ammonia and hydrogen gases are released and silicon nitride can be produced.

As mentioned above, the recovery of the intermediate product requires the residual [NnH(
n+1)]1 by solvent evaporation of the reactant. [NnH(n□)]1 When the reactant is hydrazine, the product is a clear, stable solution that precipitates a white residue upon evaporation. When this solution is subjected to infrared analysis,
Peak of N-N stretch (usually about 1098 cm-'
) is divided into two peaks of the same intensity, 1050 and 1120c+++-'. This results from 5t-N association in solution. In addition, the obtained spectrum is 0 for elements other than silicon, nitrogen, and hydrogen.
．． There were no elements present in amounts greater than Q5 vt, %, indicating that the solution was highly pure.

After evaporation of the solvent, the amorphous intermediate powder residue is heated in a non-reactive atmosphere such as argon to a temperature range of about 1200°C = 700°C, and the residue is then maintained at this temperature for at least about 15 minutes up to about 2 hours. By making high purity crystalline alpha silicon nitride (St3N4), i.e. at least 99.9 wt.%, preferably 99.995
An alpha silicon nitride product can be produced with a purity of % wt'. Although longer heating times may be used, it does not appear that much time is required to completely convert the residue to form Alpha 513N4 with a particle size range of about 0.01 to 0.5 microns. To determine that the final product is alpha silicon nitride,
You can also check the purity of the cations in the substance. This is because, by high-temperature heat treatment, amorphous silicon nitride with relatively low purity generally produces beta-type silicon nitride in addition to alpha-type silicon nitride. On the other hand, if beta silicon nitride is required, this can be achieved by adding an agent known to promote the production of the beta form.

<Example> The present invention will be described in detail below with reference to Examples.

Example 1 Ammonia gas was placed in a polyethylene bottle and liquefied using dry ice at about -78°C for 6 hours to produce 50ml of liquid ammonia. The liquid ammonia was then contacted with 5 g of granular silicon with a particle size of less than 1 micron and a purity of 99.9 wt.%. These reactants were milled in a reaction vessel for 3 hours and -78
The reaction was carried out at ℃ for 48 hours. The intermediate was recovered as a brown residue by evaporating residual NH3. This residue was found to be amorphous by X-ray diffraction. However, some unreacted silicon was present, which gave it a brown color. When this residue was subjected to infrared spectroscopy, it showed peaks different from the IR reference pattern for silicon. The sharp absorptions associated with the NH and NF2 groups are 11' = 1180, 1210, and 8000(7)-
■It was recognized. Also, a high shoulder between 980=05105O' due to the wide 5i-N stretch was observed. Observation of the residue using a scanning electron microscope (sm+o) revealed amorphous materials dispersed between silicon particles.

The residue was heated to a temperature of 1800° C. for 2 hours under an argon atmosphere. To prevent possible oxygen contamination, the crucible was double-walled and the inner crucible wall was covered with silicon nitride powder. The X-ray pattern of the obtained product is 1
Alpha silicon nitride and unreacted silicon at 000°C are shown. SIEM IED that only produced alpha silicon nitride at 1400°C and discovered only silicon
The S analysis (nitrogen cannot be detected) confirms that the reaction product is highly pure.

Example 2 In 50 ml of liquid hydrazine, 0.05% granular silicon, average particle size 10 microns or less, purity 99.9 wL,
g was added. This mixture was allowed to react for 3 hours at 25° C. in an inert argon atmosphere in a reaction vessel. The resulting reaction product was a clear solution containing silicon, as determined by inductively coupled plasma atomic absorption.

Vacuum solvent evaporation of hydrazine left a polymeric residue.

This residue is due to the 5i-N stretch.
II-l Tenonatsu R absorption hunt, 110l100=22(
A wide N-N stretch between 1', NH, NF2 groups on the I250l = 600 side and 2800-
3500 ■ = exhibits wags and antisymmetric stretching due to wide stretching of the area, respectively.

This product gives rise to a broad band Raman peak centered at 800 cm-', which flattens on exposure to air. When this residue is heated in air, 5i
-N, NH, and N H2 groups disappear, and 1000 countries
is replaced by SiO. This Si/N2H4 intermediate complex also has a
8rv's wide shoulders absorb UV rays. The near-UV transition at 288n- shows some double-bonded nitrogens, i.e. -N-N-, due to the electronic transition from the p1 orbital state to the antibonding pi orbital state. The electronic transition from the ground state to the antibonding sigma orbital state, which is normally observed at 220r+m in silanyl/hydrazine complex compounds, is at 240r+m.
Due to the large number of nitrogen-nitrogen bonds, back-donation from nitrogen to silicon is prevented. Thermogravimetric analysis of the residue showed a loss of 79vt,%. This loss corresponds to approximately 6 N 2 H4 for each silicon atom. X-ray diffraction analysis of the intermediate product showed it to be amorphous. SUN test results showed that the intermediate product residue after evaporation was a fine colloidal powder.

The residue was heated at 1400"C for 3 hours in an argon atmosphere with a nitrogen buffer as described in Example 1.

Fine white crystals were recovered which X-ray diffraction showed to be alpha Si3N4.

Example 3 To further characterize the intermediate compound formed by the reaction of elemental silicon with the [NnH(n+1)]1 reactant, the local silicon environment was analyzed by silicon NMR to determine the The types of chemical bonds present within the intermediate products were investigated. -73,1pp- and -82,08
A peak was found at pp-, which is specific to the silicon-nitrogen bond. No other particularly large peaks were observed, indicating that silicon-nitrogen-hydrogen bonds are predominant in this intermediate compound. In particular, the absence of silicon-hydrogen bonds means that INEPT
Cross Po1arizatIon Tech-
Confirmed using nlques. This method is described in the Journal ol' Magnet
Ic Re5o-nance, Vol, 55 (
1983), Po1a published in PP, 51-83.
rlzatln Transfer'er Between
Two 5calar-Coupled 5yste
ls of Arbltrary Numbers
of'Nucle of' Arbitrary
DavldT, Pegg and M,R entitled ``5p1ns''
See the paper by Bendall.

This sample was also analyzed by proton NMR. This proton chemical shift is typically a well known method in the analysis of silyl-amines. This analysis shows that the hydrogen is bonded to silicon through nitrogen, not a simple nitrogen-hydrogen bond as in the hydrazine solvent. This results in elemental silicon. Furthermore, since silicon NMR analysis did not show a direct silicon-hydrogen bond, it is believed that the intermediate compound consists of a compound having a silicon-nitrogen-hydrogen bond.

The method for producing high-purity 513N4 and its precursors according to the present invention has been described above with reference to specific examples, but the process and equipment, as well as the parameters and materials used, may be modified in various ways within the scope of the claims. It will be obvious to those skilled in the art that modifications and variations are possible.

[Brief explanation of the drawing]

The accompanying drawing is a flow sheet showing an embodiment of the method of this invention. Patent applicant Yukio Omata

Claims (1)

[Claims] 1. Elemental silicon is converted into liquid nitrogen represented by the following formula:
Hydrogen reactant [N_nH_(_n_+__m_)]_l In the formula, n = 1-4; m = 2 when the nitrogen-hydrogen reactant is linear, m = 0 when the nitrogen-hydrogen reactant is cyclic, and react at low temperature. A method for producing a high-purity substance consisting of silicon, nitrogen, and hydrogen, characterized by: 2. The elemental silicon has a mass of 99.9wt. when n=1.
% purity and 95 wt.% when n=2-4. % purity.